Mobile broadband is expected to contribute substantially to a continued spreading of Internet access; either as complement to, or substitute for, wireline broadband access. Similar to the formidable success of mobile telephony, it is envisaged that the 3rd Generation Partnership Project (3GPP) family of standards will contribute substantially to a high penetration of mobile broadband globally. While mobile communication standards, such as GSM/GPRS/EDGE has been the most successful system for mobile telephony and rudimentary data access, LTE is becoming an attractive technology in the longer term, High Speed Packet Access (HSPA)—including High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA; also known as Enhanced Uplink, or EUL)—will in many markets be the primary mobile broadband technology in the future.
Nowadays, in order to increase the downlink transmission throughput of mobile communication systems, Downlink Multi-Carrier (DLMC) was introduced by 3GPP to provide higher speed downlink packet service and to increase the downlink capacity. For example, the Global System for Mobile Communication (GSM) system seeks to provide a comparable transmission speed as 3G (e.g. TD-SCDMA, CDMA2000) system by employing the Downlink Multi-Carrier (DLMC) technique.
In the mobile communication systems, wireless signals usually suffer various distortions, such as fading, interference, frequency error, and timing error, etc., which degrade the performance of the mobile communication systems. Therefore, timing synchronization and frequency synchronization are extremely important for the mobile communication systems because of their sensitivity to the timing and frequency errors. To guarantee the fast and accurate data transmission, the Inter Symbol Interference (ISI) and Inter Carrier Interference (ICI) caused in the transmission have to be eliminated as much as possible. In the real world, frequency offsets will be arising from the frequency mismatch of oscillators of a transmitter and a receiver and from existence of Doppler shift in channels. In addition, due to the delay of signal when transmitting in the channels, the receiver in general starts sampling a new frame at the incorrect time instant. Therefore, it is important to estimate the frequency offset to minimize its impact, and to estimate the timing offset at the receiver to identify the start time of each frame.
In the conventional DLMC-related mobile communication systems, typically more than one Absolute Radio Frequency Channel Numbers (ARFCN) is used to transmit signals to one Mobile Station (MS), and each channel is treated independently during the timing offset estimation and frequency offset estimation. Since different channels with different ARFCN usually undergo different fading and interferences, if one channel suffers from a relatively strong interference, the timing offset estimation and frequency offset estimation for this channel will be unreliable, which degrade the entire synchronization performance of this channel.